Vibrations can be very odd things to pin down. To answer your question, yes it is possible to have a drive shaft vibration in one gear and not another, even at the same speed. For one, there is much more torque when you are in the lower gear. The extra torque could prevent the vibration, or in another instance cause it.


Harmonic oscillations are strange beasts, as there are so many contributing factors in setting them up. The bottom line is, if something gets excited at the same frequency as the resonant frequency, it will vibrate. The resonant frequency can be changed by almost anything. The weight, the mounting, etc..... It's like the classic opera singer cracking a wine glass stunt. If you excite the material at the same frequency as its resonance (or a harmonic thereof) the energy will start an oscillation.


So in other words, something has changed. I like the suggestion of the out of phase driveshaft coupling. Very likely. It is also possible that the flex joints deteriorated from being disconnected and re-attached.

Check all the rubber parts; trans mount, drive shaft mounts, differential mount, engine mounts, flex joints. All could possibly contribute to your oscillation.


-tp